Field of the Invention
The present invention relates to an image pickup apparatus such as a surveillance camera, and in particular to an image pickup apparatus that is resistant to environments and used in low-temperature environments and environments where temperature widely varies, and an image monitoring system.
Description of the Related Art
A surveillance camera which is able to remotely monitor an image is required to be resistant to environments such as a sudden temperature change of an installation environment and installation in a place below freezing.
A sudden temperature decrease of an installation environment causes condensation to form inside a surveillance camera, and in particular, condensation on an image pickup means and a light transmissive cover, which protects the image pickup means, leads to a degradation in a sharpness of a captured image. In a surveillance camera that has high airtightness so as to ensure water resistance, moisture contained in air in a case resists shifting to outside, and hence condensation tends to occur.
Further, in a low-temperature environment such as below freezing, moisture included in air inside the case of the surveillance camera tends to escape due to a decrease in saturation water vapor pressure, and hence condensation tends to occur and freeze into frost. Therefore, measures against frosting as well as condensation need to be taken. Moreover, in a low-temperature environment, changes in conditions of sliding portions, fitting portions, and areas concerned with ease of sliding such lubricating oil in a lens drive unit for a focus lens, which constitutes an image pickup means, and other drive units may lead to degradation of focusing performance. For this reason, the sliding portions, fitting portions, and areas concerned with ease of sliding such lubricating oil need to be heated to a predetermined temperature so as to avoid a degradation of focusing performance.
To adjust a temperature inside a camera case, there has conventionally been proposed a technique according to which a wind passage is provided around a lens barrel to efficiently prevent condensation so that warmed air can positively strike a front window in a front area of an image pickup means as seen in a direction of an optical axis (see Japanese Patent No. 5776020).
When a surveillance camera is started in a low-temperature environment such as below freezing, electric components such as an image pickup device and a power source are heated to high temperatures, and hence moisture frosted on surfaces of those electric components is evaporated into air. Due to waterproofing performance, the evaporated moisture wafts in inside air without escaping to outside, touches the front window that has been cooled to below freezing, and precipitates as frost. This may lead to degrading a sharpness of a captured image.
According to Japanese Patent No. 5776020, however, causing air including moisture to positively striking the front window fosters precipitation of frost. Moreover, in order to melt frost that has been formed, all of air inside the case needs to be satisfactorily warmed, and hence it may take time until frosting or condensation is eliminated.
Similarly, when sliding portions of a lens drive unit and others are desired to be warmed, all of air inside the case must be satisfactorily warmed. Therefore, it takes time until the sliding portions are warmed, and hence it may take time until an image with high sharpness is obtained.